1. Field of the Invention
The disclosure generally relates to a method and apparatus for depositing a substantially solid film onto a substrate. More specifically, the disclosure relates to a novel method for printing an Organic Light-Emitting Diode (“OLED”) film using a facetted rotating source or a drum.
2. Description of Related Art
In printing electronic films it is important to deposit a dry film onto a surface so that the material being deposited forms a substantially solid film upon contact with the substrate. This is in contrast with ink printing where wet ink is deposited onto the surface and the ink then dries to form a solid film. Because the inking process deposits a wet film, it is commonly referred to as a wet printing method.
Wet printing methods have two significant disadvantages. First, as ink dries, the solid content of the ink may not be deposited uniformly over the deposited area. That is, as the solvent evaporates, the film uniformity and thickness varies substantially. For applications requiring precise uniformity and film thickness, such variations in uniformity and thickness are not acceptable. Second, the wet ink may interact with the underlying substrate. The interaction is particularly problematic when the underlying substrate is pre-coated with a delicate film. An application, in which both of these problems are critical is the deposition of organic light-emitting diode (“OLED”) films.
The problem with wet printing can be partially resolved by using a dry transfer printing technique. In transfer printing techniques in general, the material to be deposited is first coated onto a transfer sheet and then the sheet is brought into contact with the surface onto which the material is to be transferred. This is the principle behind dye sublimation printing, in which dyes are sublimated from a ribbon in contact with the surface onto which the material will be transferred. This is also the principle behind carbon paper. However, the dry printing approach introduces new problems. Because contact is required between the transfer sheet and the target surface, if the target surface is delicate it may be damaged by contact. Furthermore, the transfer may be negatively impacted by the presence of small quantities of particles on either the transfer sheet or the target surface. Such particles will create a region of poor contact that impedes transfer.
The particle problem is especially acute in cases where the transfer region consists of a large area, as is typically employed in the processing of large area electronics such as flat panel televisions. In addition, conventional dry transfer techniques utilize only a portion of the material on the transfer medium, resulting in low material utilization and significant waste. Film material utilization is important when the film material is very expensive. An application where all of these problems are particularly pronounced is, again, the OLED film deposition.
Therefore, there is a need for a method and apparatus to provide, among others, a non-contact, dry technique for depositing an OLED film that overcomes these and other disadvantages and shortcomings.